Cytoplasmic streaming velocity as a plant size determinant.

This analysis is noteworthy, as it suggests that cytoplasmic streaming velocity can be a limiting factor for cellular growth in plants. The phenomenon of cytoplasmic streaming is well described across a wide range of plant species and is thought to promote the movement of small molecules through the plant cell beyond that possible through just passive diffusion. In keeping with this hypothesis, a good correlation exists across species between larger cell sizes with higher rates of cytoplasmic streaming, which in turn can be related to characteristic differences in the activity of myosin XI. In this study, the authors demonstrate that chimeric forms of myosin XI derived from a green alga, Chara, which has high streaming velocity, confer elevated rates of streaming compared to wild-type when introduced into Arabidopsis and, surprisingly, significantly higher rates of cellular growth. In parallel, engineered forms of myosin XI derived from humans that reduced streaming velocity were shown to reduce growth rates. Although no specific explanations are offered for how higher rates of cytoplasmic streaming lead to higher growth rates, this study does highlight a cellular parameter that is typically overlooked in experimental and theoretical work aimed at modelling growth.